Slurry wall
From Wikipedia, the free encyclopedia
A slurry wall is a type of wall used to build tunnels, open cuts and foundations in areas of soft earth close to open water or with a high ground water table.
A set of guide walls, typically 1m (3 feet) deep and 0.5m (1.5 feet) thick, is first constructed on the surface. A special clamshell-shaped digger is used to excavate the slurry trench guided by the guide wall. The trench is kept filled with slurry (a mixture of bentonite and water) at all times to prevent collapse. Once the first trench is completed to design depth, or bedrock, an adjacent trench is dug in the same manner. Eventually, once a particular length is reached, a reinforcing cage is lowered into the slurry-filled pit and the pit is filled with concrete from the bottom up using tremie pipes. The concrete displaces the bentonite slurry which is pumped out and recycled.
On completion of concreting, digging within the now concrete wall-enclosed area can proceed. To prevent the concrete wall from collapsing into the newly open area, temporary supports such as tiebacks (anchors) are installed. Tiebacks are steel rods drilled through the concrete wall out into the soil or bedrock on the other side. Grout is pressure pumped into the anchor holes so that the rods become attached to bedrock or soil. Once excavation is complete, construction of the structure inside the wall can begin. When completed, the structure itself prevents the wall from collapsing and so the tiebacks may be removed.
Slurry wall construction was used to construct the "bathtub" that surrounded most of the World Trade Center site. Slurry walls were also used heavily in Boston's Big Dig tunnel project.
